another hypothesis i heard was rural kids grew up with their immune systems exposed to more stuff and so better trained/less likely to overreact. personally, i always noticed kids with allergies tended to be weak and sickly much more often, so maybe that's related.

Allergies are a form of immune response to normally innocuous things.

It makes sense that there is general coincidence between severe allergies and other immune disorders.

not just immune disorder, i mean that "allergy kids" always seemed to be the 110lb scrawny ones, never go outside, never play sports, and burst in to tears for things that made other kids say "ow". idk but makes it seem like maybe there's as much nurture as nature here, i bet

ngl i think this is just a epigenetic shift from people who have been "raised weak" for several generations. i can't prove it completely but there is some research showing that kids with milk allergies end up runty:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4362703/

https://www.jacionline.org/article/S0091-6749(19)31475-7/ful...

Milk allergies and intolerance are often genetic.

By the way, the two worst offenders i ever met when talking about allergies were around the same age (they should be in their 60s now) and both are Distilben babies. And they were scrawny, but it wasn't by choice, they just couldn't eat most fats. Nothing to do with nurture in their case.

Yeah, i had horribles allergies as a kid, then it got better (i'm from a rural area, then moved to an even more rural area), so i guess there might be individual variance too. My allergies are sightly worse now that i live in a big coastal city (80k in winter-120k in summer), but i never found any evidence.